1. Field of the Invention
The present invention relates to a method for manufacturing fluorescent display screen cathodes including microtips, as well as the product obtained with this method.
2. Discussion of the Related Art
The invention relates to the industrial field of flat display screens with matrix addressing, and more particularly to display screens using the microtip technology, i.e., screens having a vacuum tube formed by two thin glass plates, the back plate, or cathode plate, including a matrix array of field effect emitters which are deposited in accordance with thin-film techniques, and the front plate, or anode plate, being coated over its inner surface with a transparent conductive layer bearing phosphor elements.
In such screens, in front of each anode pixel, is formed a large number of microtips, constituting an emitting surface. This emitting surface is defined by the intersection of a row (grid conductor) and a column (cathode conductor) of the matrix.
The cathode of a conventional microtip screen is essentially formed by four layers which are successively deposited onto a glass or silicon substrate, and etched, namely: a conductive layer playing the role of cathode "column conductors"; a resistive layer, generally made of silicon, for limiting the value of the emission current; an insulating layer; and a second conductive layer constituting the grid "row conductors". After deposition of these layers, holes are etched in the grid and in the insulating layer and microtips are formed therein.
In conventional methods, at least four (and preferably five) masking and photoetching operations are necessary for the fabrication of the layers constituting the cathode, namely: etching the cathode columns, etching holes, etching the grid rows, etching the cathode contacts and, preferably, partially etching the resistive layer between the cathode columns to prevent leakages and column coupling.
In addition, the images formed by a microtip display screen are usually observed through the anode plate. So, it is the surface bearing the phosphor elements, opposite to the surface which receives the electrons, i.e., with the lowest brightness, which is seen.